Abstract 1195 Poster Session II, Sunday, 5/2 (poster 55)

Elevated levels of proinflammatory cytokines have been demonstrated in blood and tissue samples from babies with NEC. The precise role played by bacteria in such events is not clear. We have previously reported that adherent E. coli can cause NEC-like injury in a rabbit ileal loop model and that Gram (+) bacteria (E. faecium) can block such injury. We also have shown elevated levels of IL-8, IL-1β and IL-1 receptor antagonist (IL-1RA) in E. coli-infected ileal loops.

In the present study, we compared the expression of cytokine mRNA in response to defined Gram (-) (E. coli) and Gram (+) (E. faecium) bacterial insults in rabbit ileal loops, in an attempt to examine the role of cytokines in the disease pathogenesis. Three different groups of animals were infected with either (i) E. coli, (ii) E. faecium or (iii) a combination of E. coli + E. faecium (co-infection). In each animal, multiple loops were infected with bacteria and control loops received PBS. Diseased and control ileal tissue was obtained from 4-5 loops (each animal) from 3-6 rabbits in each group, 12-18 hours after bacterial infection. Expression of cytokine mRNAs was examined by RT-PCR using rabbit specific primers and quantified in a fluorimager. Each cytokine was normalized against β-actin. In E. coli-infected loops, the mean value of IL-8 was 0.39 ± 0.05(SEM) compared to 0.19 ± 0.04 in controls [p < 0.05]. For IL-1β the mean value was 0.10 ± 0.01 compared to 0.04 ± 0.005 in controls [p < 0.001]. In co-infected loops, the mean value for IL-8 in infected loops was 0.13 ± 0.04 compared to control 0.12 ± 0.07) [p = NS]. IL-1β levels were also not significantly increased in co-infected loops (0.22 ± 0.04 vs. 0.27 ± 0.04; in controls) [p = NS]. IL-6 levels were similar to control in E. coli- and co-infected loops. While IL-1RA was increased by 50% in E. coli-infected loops, no significant change was seen in co-infected loops. No apparent change was noted in the expression of any of these cytokines in the loops infected with E. faecium.

These results demonstrate that specific Gram (+) bacteria (E. faecium) may exert their protective effect against Gram (-) bacteria-induced injury via blockage of proinflammatory cytokines.

Supported by a grant (HD-29735) from NICHD